Capacitive touch panels can be divided by their trace arrangements and positioning methods into the all-point type and the two-dimensional type. An all-point capacitive touch panel includes a plurality of discrete sensors arranged in a matrix and connected to a detector circuit via their respective independent traces. Such a capacitive touch panel, though capable of yielding precise positional information of objects placed thereon, is disadvantaged by high costs and a huge amount of data calculation resulted from the large number of sensors and traces used.
On the other hand, a two-dimensional capacitive touch panel, also known as an X-Y projected capacitive touch panel, as shown in FIG.FIG. 1, includes sensors composed of intersecting X-traces and Y-traces, and an X-Y projected sensing circuit can be used to convert the capacitance variations measured from the X-traces and Y-traces into digital information and thereby generate measured values along X-axis and Y-axis for object positioning for the capacitive touch panel. There are self-capacitance on each X-trace, self-capacitance on each Y-trace, and mutual capacitance between an X-trace and a Y-trace intersecting to each other, which will be influenced when a conductor approaches thereto. As shown in FIG.FIG. 2, the positioning method of such a capacitive touch panel is carried out by sequentially sensing the capacitance variations of the X-traces and Y-traces, identifying the X-axis position X1 and the Y-axis position Y1 of a finger 10 separately, and combining the X-axis position X1 and the Y-axis position Y1 into coordinates (X1,Y1) for the touch point. For single-finger applications, this positioning method can rapidly generate the coordinates of the finger 10 with a relatively small amount of calculation. For multi-finger applications, however, this positioning method may cause ghost point phenomenon. For example, referring to FIG.FIG. 3, when fingers 12 and 14 simultaneously touches an X-Y projected capacitive touch panel, there will be sensed significant capacitance variations at positions X1, X2, Y1 and Y2., thereby resulting in four touch points (X1,Y1), (X1,Y2), (X2,Y1) and (X2,Y2), of which (X1,Y1) and (X2,Y2) are ghost points, i.e., points that are not actually touched. Because of the ghost point phenomenon, the sensing circuit of an X-Y projected capacitive touch panel can not correctly identify the real points of the fingers.
The conventional all-point and X-Y projected capacitive touch panels have their own advantages and drawbacks. The X-Y projected sensing circuit measures the difference of self-capacitance lumped on X-traces and Y-traces, and has high frame rate and low power consumption, but is bothered by ghost point phenomenon. The all-point sensing circuit measures the difference of mutual capacitance between X-traces and Y-traces, and is multi-finger ghost free, but has low frame rate and high power consumption. The present invention provides positioning methods for carrying out all-point sensing on an X-Y projected capacitive touch panel, and combines the positioning methods with the conventional X-Y projected sensing to reduce the amount of calculation to provide complete positional information and eliminate the ghost point problem associated with the X-Y projected capacitive touch panels.